For over thirty years SuitAbility sold sewing patterns to make riding apparel and horse equipment. The owner retired and now only a limited number of remaining patterns are available from this source while supplies last:
Field's Fabrics Amazon.com
store (search for SuitAbility equestrian patterns)
Versions of some paper patterns are available in downloadable PDF format in the Etsy store SuitAbility Epatterns
. 56 different PDF patterns are available for western and English apparel, horse clothing, saddle pads, stable gear, and horse costumes.